1. Field of the Invention
The present invention relates to an automatic grease supply device for supplying a lubricant such as grease in order to prevent wear of sliding surfaces and rotating surfaces of movable portion of an injection molding machine.
2. Description of the Related Art
In the injection molding machine, it is necessary to supply grease at regular or irregular intervals to avoid insufficient lubrication in order to prevent wear of sliding surfaces and rotating surfaces of movable portions such as a ball screw, bearings, and a toggle bushing.
Insufficient supply of grease and insufficiency of lubrication causes mechanical problems, whereas excessive supply of grease causes problems such as adhesion of the grease to a molded article and increase in grease consumption. Because a lubricated state changes due to loads on movable portions, moving speeds of the movable portions, and moving times of the movable portions, a technique for measuring these physical amounts to automatically supply grease so as to supply the grease at the optimum time has been proposed conventionally.
Japanese Patent Application Laid-Open No. 3-793250 discloses a technique for detecting insufficiency of lubrication based on a voltage corresponding to an armature current from a current detector for detecting the armature current of a servomotor for driving a movable portion to supply the grease.
Japanese Patent Application Laid-Open No. 2000-190375 discloses a technique for supplying the grease according to an operating time of an injection molding machine and the total number of cycles and a technique for supplying the grease according to a product of a stroke and the number of cycles.
Japanese Patent Application Laid-Open No. 2008-261394 discloses a technique for obtaining physical amounts related to a movable member and representing values such as largest values and smallest values of the physical amounts and anticipating insufficiency of lubrication based on time-series variation of the representing values to supply the grease.
With the technique disclosed in Japanese Patent Application Laid-Open No. 3-793250 described above, variation in a mechanical resistance (load) due to variation in the lubricated state of the movable portion is kept track of based on the voltage corresponding to the armature current from the current detector for detecting the armature current of the servomotor for driving the movable portion and therefore it is possible to directly keep track of the variation in the lubricated state. However, magnitude of the voltage corresponding to the armature current varies also due to a change in operating conditions such as a change in a molding speed or a mold of the injection molding machine other than lubricated state and it is difficult to know optimum grease supply timing based on error voltage only. This is true in the technique disclosed in Japanese Patent Application Laid-Open No. 2008-261394 described above and it is extremely difficult to determine whether the change in the physical amount is caused by the insufficiency of lubrication or other factors in injection molding in which molding conditions are changed frequently depending on differences in the mold and resin.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2000-190375 described above, the grease supply timing is obtained based on the number of cycles, time, or the product of the stroke and the number of cycles and therefore it is possible to supply the grease according to an actual operating state of the machine. However, the grease is supplied irrespective of magnitude of the load and therefore it is difficult to completely avoid insufficiency of lubrication and excessive lubrication.